Plain bearing provided with a friction coating and method for making same

ABSTRACT

A high-performance plain bearing provided with a friction coating including a bronze layer whereof the pores are filled with a PTFE-type fluoroplastic paste filled with molybdenum bisulphide. The production method includes sintering a layer of bronze powder on the metal support of the bearing, a vacuum ionic cleaning, applying a filled fluoroplastic film, passing the component through a die and after sintering the paste, a final pass in the die for final dimensioning. During sintering and passing through the die an anti-adhesive and wear-resistant coating, based on titanium nitride or the like, is applied on the equipment.

The present invention relates to a plain bearing equipped with afriction coating and to the method for producing said coating.

High-performance plain bearings are needed in various fieldsparticularly in the reduction gearboxes of turbojet engines with highbypass ratios.

The search for high performance has led to the proposal of variousimprovements to plain bearings. Hence, U.S. Pat. No. 3,644,105 describesa bearing comprising a composite coating of copper and molybdenumdisulfide obtained by electrolytic codepositon. A surface layerconsisting of a lead-based alloy containing tin and copper completes thecoating.

The earlier known solutions are not, however, entirely satisfactory and,particularly in the applications mentioned herein above, there is stilla need to develop plain bearings that provide good operating conditionsand good service life after the corresponding severe conditions of use.These conditions in particular include resistance to very high pressure,operation at high linear speed, resistance to high temperature and theplain bearings also have to be capable of operating with lubrication bya low-viscosity oil and, for short periods, without oil.

These results are obtained satisfactorily according to the invention bya high-performance plain bearing equipped with friction coatingcharacterized in that the coating comprises a layer of bronze obtainedby sintering and the pores of which are filled with a fluoroplasticpaste filled with molybdenum disulfide.

Said friction coating is obtained in a way that is remarkable accordingto the invention using a method characterized in that it involves thefollowing steps:

-   (a) sintering a layer of bronze powder onto a metallic support under    a reducing atmosphere using tooling comprising a non-stick and    wear-resistant coating;-   (b) ionic cleaning under vacuum to activate the surface of the    sintered bronze layer without increasing the roughness of the layer;-   (c) applying a layer of fluoroplastic paste of the PTFE type filled    with molybdenum disulfide to the sintered bronze surface and    installing into a die the support coated with the sintered bronze    layer;-   (d) passing the component consisting of the coated metallic support    into the die with the addition of a non-stick and wear-resistant    coating so as to compress the paste applied in step (c) into the    pores of the sintered bronze layer;-   (e) drying the paste;-   (f) passing the component a second time through the die with the    addition of a non-stick and wear-resistant coating;-   (g) sintering the paste under determined duration and temperature    conditions followed by immersion in water;-   (h) passing the bearing component a final time through a die    equipped with a non-stick coating so as to achieve its end    dimensions.

Particular conditions of production and advantageous parameters are alsodetermined.

Other characteristics and advantages of the invention will be betterunderstood from reading the description which will follow of oneexemplary embodiment of the invention, with reference to the attacheddrawings in which:

FIG. 1 depicts, in view in longitudinal section, the metallic support ofthe plain bearing according to the invention during one step in itsproduction;

FIG. 2 depicts, in view in longitudinal section, the metallic support ofthe plain bearing according to the invention during another step in itsmanufacture.

A plain bearing especially intended for aeronautical applications suchas the reduction gearboxes of turbojet engines with high bypass ratioscomprises, in a conventional way, a metallic support schematicallydepicted as 1 in FIG. 1. The method of producing a friction coating on aplain bearing according to the invention involves a prior step:

-   (a1) electrolytic deposition of a layer 2 of copper onto the    metallic support 1, followed by tinning.

As depicted in FIG. 1, the metallic support 1 thus coated is then placedin a container 3, forming around the support 1 of the receptacle inwhich bronze powder is placed for carrying out step (a) of the methodaccording to the invention:

-   (a) sintering a layer 4 of bronze powder onto the metallic support    1, under conditions known per se of temperature and reducing    atmosphere and using tooling comprising a non-stick and    wear-resistant coating.

The next step (b) of said method consists in ionic cleaning under vacuumso as to obtain activation of the sintered bronze layer.

In step (c), a layer about 1 mm thick of fluoroplastic paste of the PTFE(polytetrafluroethylene) type filled with molybdenum disulfide isapplied to the entire sintered bronze surface and the support 1 coatedwith the sintered bronze layer 4 is then placed in a die 5, as depictedschematically in FIG. 2; next, in step (d), the component 1 consistingof the coated metallic support is passed through the die 5 with theaddition of a non-stick and wear-resistant coating so as to compress thepaste applied in step (c) into the pores of the sintered bronze layer.The coating used may, in particular, be based on titanium nitride or maybe a coating with equivalent properties such as one based on zirconiumnitride, chromium nitride or possibly aluminum nitride. This coatingavoids the sintering of the bronze onto the tooling and avoids thedisadvantages of other products known earlier such as graphite whichcontaminates the bronze and damages the adhesion of the bronze to themetallic material of the support. The same coating is also used in step(a) during sintering for the same reasons.

In the next step (e), the paste is dried, something which may, forexample, be performed at 90° C. for 2 hours. In step (f) the bearingcomponent 1 is shaped by passing it a second time into the die with theaddition of the non-stick and anti-wear coating as defined above. Step(g) of sintering the paste is then carried out under determinedconditions such as at 375° C. for 40 minutes and the component is thenimmersed in water.

Finally, in the final step (h) the bearing component 1 is passed throughthe die, still equipped with the non-stick coating, to size it to itsend dimensions.

No further machining of the plain bearing thus obtained is needed. Thequalities of adhesion to the support and the anti-friction qualities ofthe coating according to the invention thus obtained allow the plainbearing to satisfy the high performance demanded for its operation. Inparticular, the plain bearing obtained resists very high pressures thatmay exceed 50 mPa in the oil film. It can operate at high linear speedsand at temperatures up to 120° C. It tolerates low-viscosity oil down to5×10⁻⁶ m²/s at 100° C. and the bearing is capable of operating withoutoil for short periods, at reduced load.

1-4. (Canceled).
 5. A method for making a friction coating on ahigh-performance plain bearing, comprising: (a) sintering a layer ofbronze powder onto a metallic support under a reducing atmosphere usingtooling comprising a non-stick and wear-resistant coating; (b) ioniccleaning under vacuum to activate a surface of the sintered bronze layerwithout increasing roughness of the sintered bronze layer; (c) applyinga layer of fluoroplastic paste of PTFE type filled with molybdenumdisulfide to the sintered bronze surface and installing into a die thesupport coated with the sintered bronze layer; (d) passing a componentof the coated metallic support into a die with addition of a non-stickand wear-resistant coating to compress the paste applied in the applying(c) into pores of the sintered bronze layer; (e) drying the paste: (f)passing the component a second time through the die with addition of thenon-stick and wear-resistant coating; (g) sintering the paste underpredetermined duration and temperature conditions followed by immersionin water; and (h) passing the component a final time through a dieequipped with a non-stick coating to achieve its end dimensions.
 6. Themethod for producing a friction coating on a plain bearing as claimed inclaim 5, wherein the non-stick and wear-resistant coating used in thesintering (a), the passing (d), the passing (f) and the passing (h) isbased on titanium nitride or on a nitride with equivalent propertiessuch as zirconium nitride, chromium nitride, or aluminum nitride.
 7. Themethod for producing a friction coating on a plain bearing as claimed inclaim 5, wherein in the drying (e) the drying of the paste is performedat 90° C. for two hours and in the sintering (g) the sintering of thepaste is performed at 375° C. for 40 minutes.
 8. The method forproducing a friction coating on a plain bearing as claimed in claim 6,wherein in the drying (e) the drying of the paste is performed at 90° C.for two hours and in the sintering (g) the sintering of the paste isperformed at 375° C. for 40 minutes.
 9. The method for producing afriction coating on a plain bearing as claimed in claim 5, furthercomprising before applying the bronze powder: (a1) electrolyticdeposition of copper onto the metallic support under conditions knownper se, followed by tinning.
 10. The method for producing a frictioncoating on a plain bearing as claimed in claim 6, further comprisingbefore applying the bronze powder: (a1) electrolytic deposition ofcopper onto the metallic support under conditions known per se, followedby tinning.
 11. The method for producing a friction coating on a plainbearing as claimed in claim 7, further comprising before applying thebronze powder: (a1) electrolytic deposition of copper onto the metallicsupport under conditions known per se, followed by tinning.
 12. Themethod for producing a friction coating on a plain bearing as claimed inclaim 8, further comprising before applying the bronze powder: (a1)electrolytic deposition of copper onto the metallic support underconditions known per se, followed by tinning.